Common rail fuel systems provide a way to introduce fuel into the combustion chambers of an engine. Typical common rail fuel systems include an injector having an actuating solenoid that opens a fuel nozzle when the solenoid is energized. Fuel is then injected into the combustion chamber as a function of the time period during which the solenoid remains energized and the pressure of fuel supplied to the fuel injector nozzle during that time period.
To optimize engine performance and exhaust emissions, engine manufacturers may vary the pressure of the fuel supplied to the fuel injector nozzle. One such example is described in U.S. Patent Application Publication No. 2004/0168673 (the '673 publication) by Shinogle published Sep. 2, 2004. The '673 publication describes a fuel system having a fuel injector fluidly connectable to a first common rail holding a supply of fuel, and a second common rail holding a supply of actuation fluid. Each fuel injector of the '673 publication is equipped with an intensifier piston movable by the actuation fluid to increase the pressure of the fuel. By fluidly connecting the fuel injector to the first common rail, fuel can be injected at a first pressure. By fluidly connecting the fuel injector to the first and second common rails, fuel can be injected at a second pressure that is higher than the first pressure. The pressure of the fuel and the actuation fluid within the first and second common rails may be sensed via one or more pressure sensors and regulated through output control of corresponding pumps.
Although the fuel injection system of the '673 publication may include two different supplies of pressurized fluid that cooperate to adequately supply fuel to an engine at two different pressures, it may, however, have limitations. Specifically, because the second pressure is achieved by intensifying the first pressure, the second pressure is dependent on the first pressure. This dependency may limit the ability to shape the rate of fuel injections with the system of the '673 publication. In addition, because the pressure of the injected fuel is regulated by controlling pump output a significant distance upstream of the injectors, the actual injected pressure may lag behind a desired injected pressure. This lag in pressure may result in injection profiles that deviate from intended injection profiles.
The fuel system of the present disclosure solves one or more of the problems set forth above.